The p53 tumor suppressor gene has been strongly implicated in the process of carcinogenesis. In particular, a strong association exists between mutations of the p53 gene and a variety of tobacco-related cancers, including cancers of head and neck, where p53 mutations were observed in up to 78% of head and neck squamous cell carcinomas from patients who were chronic smokers. The origin of p53 mutations during tumor progression has been studied by determining p53 mutation incidence in premalignant lesions of various organs and may be indicative of the tumorigenic potential of these lesions. We and others have obtained preliminary data demonstrating that premalignant lesions of the oral cavity may possess mutations at the p53 locus and that this may be dependent upon the degree of lesion dysplasia and/or malignant potential. These data suggest that p53 mutation may be an early event in oral cavity cancer progression. Since mutation of the p53 gene is highly correlated with the malignant phenotype, it may be an excellent candidate for risk assessment for oral cavity cancer in individuals with oral cavity preneoplastic lesions, and may serve as an intermediate biomarker in chemoprevention trials. In addition, we have demonstrated what appears to be a direct correlation between p53 mutation incidence in oral cavity premalignant lesions and a specific risk factor for oral cavity cancer - tobacco use. This must be confirmed using a larger subset of tumor tissue samples from tobacco users and non-users. We hypothesize that mutations of the p53 gene may be an important biomarker for determining the tumorigenic potential of premalignant lesions of the oral cavity. The overall goal of this research proposal is to examine the incidence of p53 mutations in premalignant lesions of the oral cavity and correlate this incidence with; i) the known tumorigenic potentials of different oral cavity premalignant lesion classes, ii) the degree of lesion dysplasia, and iii) specific risk factors. Premalignant oral cavity lesion samples will be obtained from patients recruited from five collaborating centers. Lesion tumorigenic potential will be assessed by diagnostic classification of lesions into categories of known tumorigenic potentials, and the degree of dysplasia will be determined histologically. P53 mutations will be assayed using sensitive molecular techniques such as polymerase chain reaction/single strand conformational polymorphism and DNA sequencing. To verify the causal relationship between p53 mutations and cancer in oral cavity premalignant lesions, we will also examine a small group of oral cavity premalignant lesions (in paraffin blocks) obtained prospectively from patients who later developed oral cavity cancer. The p53 mutational incidence and spectrum in these lesions will be compared to the incidence and spectrum observed in the tumors taken from the same patients. These studies should provide us with valuable information on p53 mutation as a biomarker for oral cavity cancer progression and etiology, and should indicate whether an analysis of the p53 mutational status of these lesions may be useful for both cynical diagnosis and patient prognosis and treatment. These studies should aid in the detection of oral cavity premalignant lesions with the highest tumorigenic potential in patients, and should ultimately lead to improved and more aggressive treatment modalities for such lesions.